Method of digesting finely-divided materials.



' T. C. MEADOWS AND F. L. SAMPLE.

METHOD 0F DIGESTING HNELY DIVIDED MATERIALS. APPLICATION FILED DEC. 6, 19H3.

1 ,326,41 2. Patenfedl Deo. 30,1919.

fr l a, a; f f, f,

Inventors UQSM UNITED sTATEs PATENT oEEIcE.

THOMAS C. MEADOWS, OF NEW YORK, N. Y., AND FRANK L. SAMPLE, OF TEANECK, NEW JERSEY, ASSIGNORS TO AMERICAN POTASH CORPORATION, 0F NEW YORK, N.l Y., A

CORPORATION OF VIRGINIA.

METHOD OF DIGESTING FINELY-DIVIDED MATERIALS.

Specification of Letters Patent.

Patented Dec. 30, 1919.

Application led December 6, 1918. Serial No. 265,606.

'United States, residing at New York and Teaneck, in the counties of New York and Bergen and States of New York and New Jersey, have invented certain new and useful Improvements in Methods of Digesting Finely-Divided Materials; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a method of digesting finely divided materials at high pressures, andhas for its object to provide a procedure which will be more efiicient in action and less costly to operate than those heretofore proposed. y

`With these and other objects in View the invention consists in the novel steps and combination of steps constituting the method, all as will be more fully hereinafter described and particularly pointed out in the claims.

Referring to the accompanying drawings forming a part of this specification, 1n-

which the gureis a partly sectional View of an apparatus made in accordance with this invention` A represents any suitable furnace chamber, B any suitable introductory chamber for ignitingpowdered or liquidfuel, C a set of high pressure pipes or coils, located in chamber A, and through which the material to be digested may` be forced, D a centrifugal or other pump for introducing the charge to be digested against the pressure existing in the pipes C, and H a restricted nozzle for discharging the digested materials into any suitable receiver E. F represents any suitable inlet for injecting powdered fuel into the chamber B, and for the admission of air, etc., G any suitable outlet for the products of combustion leav-A ing the chamber A, and I any suitable inlet or pipe 4for conveying the charge material to the pump D. J represents a connection between the chambers B and A, K a plurality of baffles in the chamber A', and L represents doors for the said furnace chamber A. M represents portions of the pipe coils located in planes at right angles to other portions M of said coils. The construction is such that a free circulation of the combustion gases over the coils C is had, as is indicated by the arrows.

In order that the operation of this apparatus may be more clearly understood it is said: In digesting finely divided substances, such as feldspar, green sand, etc., with lime and water for the purpose of extracting the vpotassium contents, it is now well known that high pressures, such as 200 lbs., 225 lbs. to the square inch, or higher, must be employed, or else a commercial failure re sults. It is also well known that charges of several tons of material must be dealt with at each digestion in order to make the operation a paying one. These conditions renderv it necessary to build very large digesters of the autoclave type, and when it comes to making them stand the very high total pressures to which they are subjected and to keeping them steam tight during long periods, it becomes not only a very l.serious proposition but also a costly one.

In the extraction of potash fr om a mixture of feldspar, lime and water at even 225 lbs. pressure several hours are required, and a shorter, but a relatively very long time of say one or two hours is required in extracting potassium from green sand. On the other hand, we have discovered that these relatively long periods of operation can be very greatly reduced if the pressure is increased beyond 225 lbs., Ior to say 275 lbs., 325 lbs. or higher. But such abnormally high pressures are not practicable within the limits of costs in the boiler like constructions that are now employed inautoclaves. Further, in operating the present cylindrical autoc-laves, it is necessary to first charge the vessel, heat it up to carry on the digestion, then withdraw the contents after it has cooled down, and then recharge said vessel, thus making the operation an intermittent one and consequently losing greatly in time and capacity, as well as in fuel.

In carrying out the digestion process with an apparatus such as that illustrated in the accompanying drawings, on the other hand, all the foregoing objections are avoided. That is to say, thecharge material which may consist of say equal parts of feldspar and lime, mixed with a quantity of water equal eight times the weight of the rock, or which may consist of a mixture of say equal parts of green sand and lime mixed with a quantity of water equal to say three or four times the weight of the sand, is conducted by the pipe l to the pump D which latter forces it to and through the coils C which are kept sufhciently hot Iby means of the hot gases in chamber A to produce a steam pressure higher than 225 lbs. to the square inch, and often as high as say from 27 5 lbs. to 350 lbs. to the square inch or higher in the coils C. In other words, commercial drawn pipes are fully capable of withstanding these pressures as well as the temperatures necessary to produce them. The length of the coils and the restriction of the nozzle Huarte-preferably so chosen that with the pressure employed, the material is deliveredinto the chamber E with substantially all its potassium dissolved out.

Instead of using the charges above mentioned, which produce. solutions of alkali metal hydrates, it is equally practical to use charges of say green sand, lime, calcium chlorid and water, there being enough calcium chlorid present to convert all the potassium in the char e into potassium chlorid.

ln such case, t e resulting liquor will consist of a solution of potassium chlorid instead of potassium hydrate, and it will be of a much. higher concentration than heretofore, owing to the higher pressures employed, and to the fact that reversions do not seem to take place at these higher temperatures and pressures in the case of potassium chlorid solutions, as they do with corresponding temperatures and pressures when dealing with potassium hydrate solutions. llt results that the subsequent evaporation costsare lessened because more potassium chlorid is present in a -given quantity of water than heretofore.

After the charge material has been thus digested at these higher pressures and delivered into the receptacle E, it is found to consist of a mixture of a very fine and uniform sludge andone of the albove mentioned alkali metal compound solutions. The sludge constitutes a valuable by-product for use as a cementing material in making brick, and it is therefore separated from the potassium containing solution as by filtration.

In order to facilitate the filtration ste'p it is found convenient to leave a back pressure in the vessel E of say 50 lbs., so that the solution and sludge may be readily forced out of the pipe 0 and to and through the; filter not shown.

No have further discovered that with the high pressures and temperatures disclosed above, it is perfectly practical to force the sludge or charge material continuously through the coils C, without having said material set therein. The reason for this seelIlS rasante to be that when pressures around 190 lbs. have been reached, the lime undergoes a change and the insoluble constituents of the charge bec-ome less and less liable to set and clog up the pipes as the pressures increase.

It thus results that a continuous process of the nature above disclosed is practical with-the pressures stated when it would not be practical at lower temperatures, owing to the setting of the sludge and consequent clogging of the pipes.

Again, in all processes of the character above described it is very important indeed that the material be agitated during the reaction, for otherwise, not only will the yields be cut down, but the times, of digestion will be greatly prolonged. ln the autoclaves heretofore employed, the problem of proper agitation has-not only been a vexatious one, but, also, a costly one. `With the device here described, on the other hand, it is found that the passage of the 'charge through the coils C aords a sufficient agitation to attain commercial results without other means.

lt will now be clear that with an apparatus of the character outlined we are enabled to attain the following advantageous results:

(a) We may operate at muchl higher pressures than are practical in the prior devices and, therefore, we very greatly reduce the time of digestion, as well as increase the concentration of the potassium containing liquors when using a given quantity of water.

rlhe process being a continuous one, instead of an intermittent one, as heretofore, we very greatly increase the output of` the plant, and at the same time save the heat units that have been lost in cooling Vdown the apparatus between chargesi (c) The liquors obtained being of a higher concentration for a given quantity of water, we greatly save in the costs of the subsequent evap'orations; and

(d) The chamber E being a closed one, we are enabled to utilize a steam pressure therein to aid in a continuous ltering step.

Suitable valves are or may be provided in the connections as indicated to facilitate the operation of the device.

lt is obvious that those skilled in the art may vary the details of our procedure as well as the arrangement of the parts of our apparatus7 without departing from the spirit of the invention, and therefore we do not wish to be limited to the above dis; closure except as may be required by the claims.

What we claim is 1. The process of digesting mixtures of lime, water and finely divided potassium bearing mineral materials at superatmospheri'c pressures, which consists in continuously forcing said mixtures into and, through a heated pipe coil in which saidpressures are maintained; and separating out the potassium bearing solutions thus obtained, substantially as described.

2. The process of extracting combined potassium from a naturally occurring potassium bearing mineral which consists in providing a mixture containing said mineral, lime and Water; continuously forcing said mixture to and through pipe coils in which a superatmospheric pressure is maintained While heating said materials; and separating the potassium bearing solution thus obtained from the insoluble residue, substantially as described.

3. The process of extracting combined potassium from a naturally occurring potassium ibearing mineral which consists in providing a mixture containing said mineral, lime and Water; continuously forcing said mixture to and through pipe coils in which a superatmospheric pressure exceeding 190 lbs. to the square inch is maintained While heating said materials; discharging the' digested material iny a container in which a superatmospheric pressure is maintained; and separating the potassium bearing solution thus dbtained from the insoluble residue by permitting said last named pressure to forcetle said solution through a lter, substantially as described.

4.'Tl1e process of extracting combined potassium from green sand which consists in providing a mixture containing green sand, lime and Water; continuously forcing said mixture through a coil of pipe in Which `ously forcingsaid mixture through a coil of pipe in which there is maintained a pressure exceeding 225 lbs. to the square inch While heating said pipe and mixture;

and separating out the potassium contain-A ing solution thus obtained from the insoluble residue, substantially as described.

In testimony whereof We aflix our signatures, in presence of tWo Witnesses.

THOMAS C. MEADOWS. FRANK L. SAMPLE. 

